1. Field of the Invention
This invention relates to a vehicle clutch control system including a fluid actuated operator and clutch linkage.
2. Description of the Prior Art
Typically, the clutch in an automobile or a light truck is controlled by a clutch pedal connected through a linkage to the clutch throwout bearing. However, when the clutch must transmit relatively high loads such as in heavy duty trucks and construction equipment, the force required to move the clutch pedal is sufficiently high to warrant power assist devices. In addition, for some applications it is desirable to eliminate the rigid linkages typically utilized between the clutch pedal in the vehicle cab and the clutch. For example, in the "cab over" truck the linkage must be flexible or detachable for servicing purposes. Therefore, a fluid actuated operator can be utilized to actuate the clutch with reduced pedal effort in response to control of the driver through the clutch pedal and allow the use of a flexible cable or the like between the cab and the clutch. The fluid utilized in such applications is preferrably pressurized air and is so referred to hereinafter although it will be understood that any gas or liquid can also be used.
Normally, clutch operators are connected to a pivoted link to transmit force to the throwout bearing. Most clutches have a bearing load curve that increases from full engagement to full disengagement and are readily controlled. Some clutches, generally known as declining pedal effort clutches, have a lower bearing load at full disengagement than at some point between full engagement and full disengagement. The prior art air actuated clutch operators are not satisfactory in operating such clutches.
The prior art air actuated operators can be of the type which are operated from a source of vacuum, such as the intake manifold of the vehicle engine, or of the type which are operated from a source of air under pressure where a relatively high operator force is required. The operator requires a valve for connecting to and disconnecting from the source when it is desired to actuate the clutch.
A typical prior art operator control valve includes a sleeve valve having a plunger member slidably mounted within a sleeve for movement in response to the operation of the accelerator pedal. The sleeve is provided with a first and second annular series of ports and the plunger has a triangular-shaped body to provide a recess. As the accelerator pedal is released, the plunger is moved so that the recess registers with the two sets of ports to connect the intake manifold to a pressure differential motor which disengages the clutch. As the accelerator pedal is depressed, a spring moves the plunger relative to the sleeve to close the second series of ports which disconnects the intake manifold allowing the clutch to engage. Such a control valve unit is disclosed in U.S. Pat. No. 2,152,088, issued Mar. 28, 1939 to E. R. Price et al.
Another prior art control valve unit includes a sleeve valve having a first outer sleeve, a second inner sleeve slidably mounted within the first sleeve and an operating member slidably mounted within the second sleeve. The operating member is connected to the clutch pedal by a yieldable connection. When the clutch pedal is in the engaged position, the first sleeve disconnects a clutch actuator from the intake manifold. As the clutch pedal is depressed, the operating member and the second sleeve move to close an opening between the first and second sleeves thereby closing off communication between the atmosphere and the actuator. Further depression of the clutch pedal collapses a spring holding the first sleeve in position to register a pair of ports to connect the actuator to the intake manifold. This causes a pressure differential between the ends of the two sleeves resulting in a load upon the clutch pedal directly proportional to the degree of vacuum in the actuator. If the clutch pedal is held in a partially depressed position, the sleeves will be forced in the opposite direction to close the connection between the intake manifold and the actuator to maintain the degree of clutch disengagement achieved. Such a control valve unit is disclosed in U.S. Pat. No. 2,207,827, issued Jan. 14, 1936 to V. W. Kliesrath.